Subtle, brilliant mystery
Everything Peter Dickinson has ever written is marvellous, but this is definitely one of my favourites. Like many of his mysteries, it isn't a normal detective novel, but an exploration of past events that leads to some sort of resolution. The Last Houseparty is never exactly resolved, but that's part of the reason it is so good. Exactly what happened at the last houseparty at Snailwood Castle is never explained, and never resolved.
Much of the book is set at the castle, during a glamorous house party organized by the flamboyant Zena--the last of her famed "superduperdos", sometime in the thirties. The house party, and the Snailwoods, fall apart when a child is assaulted, and a mysterious fire breaks out. Fifty years later, the child, now the owner of the abandoned estate, looks back on the events of that weekend, and tries to uncover the truth, with only the firm conviction that the man accused of assaulting her was not the perpetrator. As her memories return, the reader is plunged into a maze of conflicting motives, disparate characters, and the shambles that caused one ordinary weekend to be, indeed, the last houseparty.